A laser pulse characteristic measurement device and method based on fundamental light modulation sampling

Abstract

This invention provides a laser pulse characteristic measurement device and method based on fundamental frequency light modulation sampling, which solves the technical problem that existing measurement optical paths, due to the use of multiple transmission optical elements and the introduction of quantitative material dispersion, cannot easily and effectively measure femtosecond ultrashort pulse lasers with few periods or even single periods. The measurement device provided by this invention is equipped with a first aperture. The light from the ultrashort pulse laser to be measured passing through the large aperture of the first aperture is used as the pump light, and the light passing through the small aperture is used as the signal light. The pump light is reflected sequentially by a second reflecting mirror, a concave mirror, and a medium before being completely blocked by an obstruction. The signal light is reflected sequentially by the first reflecting mirror, a concave mirror, and a medium, and then focused onto a spectrometer through the edge region of the second aperture and a lens. By moving the delay line on the first or second reflecting mirror, the intensity of the signal light at different delays is sampled to obtain the fundamental frequency light modulation intensity curve at different delays.

Description

Technical Field

[0001] This invention relates to laser pulses, and more particularly to a laser pulse characteristic measurement device and method based on fundamental frequency optical modulation sampling. Background Technology

[0002] With the development of laser technology, femtosecond lasers have been widely applied in fields such as biomedicine, ultra-precision machining, and information science. As a more precise, accurate, and faster tool, femtosecond lasers have provided novel technological means for these fields, solving some inherent problems and becoming an important direction for interdisciplinary integration. Currently, ultrafast femtosecond lasers are quite mature, with wavelengths covering the ultraviolet to mid-infrared bands. However, how to perform comprehensive diagnosis of femtosecond laser pulses in different bands remains a very challenging and important research topic.

[0003] The pulse characteristics of lasers typically include wavelength, pulse width, and phase in the time domain, and spot quality and divergence angle in the spatial domain. Additionally, laser pulse characteristics also include energy and repetition frequency. Different pulse characteristics require different instruments for measurement, with time-domain characteristics being particularly complex. For ultrashort pulse lasers, internationally, methods commonly used include frequency-resolved optical switching, spectral phase coherence direct electric field reconstruction, attosecond fringe cameras, pHz optical oscilloscopes, and the recently developed pulse sampling method based on air tunneling ionization perturbation theory. Among these, the pulse sampling method based on air tunneling ionization perturbation theory can accurately obtain pulse spectrum and phase information, and its system optical path and algorithm are relatively simple, quickly attracting attention in the ultrafast laser field. However, its measurement optical path uses multiple transmission optical elements, introducing a certain amount of material dispersion, which means it cannot be simply and effectively measured for femtosecond ultrashort pulse lasers with few or even single periods. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problem that existing laser pulse characteristic measurement optical paths, due to the use of multiple transmission optical elements and the introduction of quantitative material dispersion, cannot easily and effectively measure femtosecond ultrashort pulse lasers with few periods or even single periods. The invention provides a laser pulse characteristic measurement device and method based on fundamental frequency light modulation sampling.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A laser pulse characteristic measurement device based on fundamental frequency light modulation sampling is characterized in that it includes a first aperture, a first reflector, a second reflector, a concave mirror, a medium, an obstruction, a second aperture, a lens, and a spectrometer.

[0007] The first aperture is located in the incident light path of the ultrashort pulse laser to be tested. The first aperture has a large aperture and a small aperture to split the ultrashort pulse laser to be tested into two beams. The transmitted light passing through the large aperture is used as the pump light, and the transmitted light passing through the small aperture is used as the signal light.

[0008] The area of ​​the large aperture needs to ensure that the transmitted pump light energy is greater than 7 μJ, and the area ratio of the small aperture to the large aperture is 1:25 to 1:36.

[0009] The first or second reflector is provided with a delay line to change the relative delay between the signal light and the pump light; the first and second reflectors are located on the same plane when the relative delay between the signal light and the pump light is 0.

[0010] The focal length of the concave mirror is chosen to ensure that the pump light focusing intensity is greater than 5 × 10⁻⁶. 12 W / cm 2 ;

[0011] The second reflector, the concave mirror, the medium, and the blocking object are located sequentially on the incident light path of the pump light; after the pump light is reflected sequentially by the second reflector, the concave mirror, and the medium, it is completely blocked by the blocking object.

[0012] The central region of the second aperture stop is shielded, while the edge region is used for transmission;

[0013] The first reflecting mirror, the concave mirror, the medium, the second aperture, the lens, and the spectrometer are located sequentially on the incident light path of the signal light; the signal light is reflected sequentially by the first reflecting mirror, the concave mirror, and the medium, and then focused onto the spectrometer by the edge region of the second aperture and the lens.

[0014] Furthermore, a gap of 1mm-2mm is maintained between the first and second reflectors;

[0015] The distance between the small hole and the large hole is greater than or equal to 2 mm.

[0016] Furthermore, the first and second reflectors are D-shaped mirrors, which are symmetrically arranged on both sides of the gap, with the side closest to the gap being a straight edge.

[0017] Furthermore, the gap between the first reflector and the second reflector is 1 mm;

[0018] The distance between the small hole and the large hole is 2mm.

[0019] Furthermore, the medium is fused silica or SiO2.

[0020] Furthermore, the second aperture is a thin glass sheet that blocks the central region and transmits light at the edge region.

[0021] Furthermore, the delay line is formed by placing the first reflector on a movable platform and moving the movable platform back and forth in a direction perpendicular to the first reflector; preferably, the movable platform is a piezoelectric ceramic displacement stage.

[0022] Furthermore, the delay line is formed by placing the second reflector on a movable platform and moving the movable platform back and forth in a direction perpendicular to the second reflector. Preferably, the movable platform is a piezoelectric ceramic displacement stage.

[0023] This invention also provides a measurement method for a laser pulse characteristic measurement device based on fundamental frequency optical modulation sampling, characterized by the following steps:

[0024] 1】Moving delay line, using pump light to perturb the light field of signal light on the surface of medium under different delays to form fundamental frequency light modulation, and sampling the light intensity of signal light under different delays by a spectrometer to obtain the fundamental frequency light modulation intensity curve under different delays;

[0025] 2】Based on the fundamental frequency light modulation intensity curves under different delays, the spectrum, phase, and pulse width information of the ultrashort pulse laser under test are obtained through an inversion algorithm.

[0026] The advantages of this invention compared to the prior art are as follows:

[0027] 1. The present invention provides a laser pulse characteristic measurement device based on fundamental frequency optical modulation sampling. The device divides the ultrashort pulse laser under test into pump light and signal light through a first aperture. By changing the relative delay between the signal light and the pump light, the intensity of the signal light under different delays is sampled. That is, the fundamental frequency light is modulated by the perturbation of the optical field of the signal light on the surface of the medium by the pump light under different delays, thereby obtaining the fundamental frequency light modulation intensity curve under different delays. The measurement device of the present invention adopts all optical devices and total reflection optical path. The system is easy to build, simple to operate, has high measurement accuracy and more comprehensive detection information.

[0028] 2. The laser pulse characteristic measurement device based on fundamental frequency light modulation sampling provided by the present invention maintains a gap of 1mm-2mm between the first reflector and the second reflector, which can avoid the influence of moving the delay line on the first reflector and thus ensure the measurement accuracy.

[0029] 3. The present invention provides a laser pulse characteristic measurement device based on fundamental frequency light modulation sampling. Both the first and second reflecting mirrors are set as D-shaped mirrors, which reduces the footprint of the first and second reflecting mirrors while forming a larger light spot.

[0030] 4. The present invention provides a laser pulse characteristic measurement method based on fundamental frequency light modulation sampling. By changing the relative delay between the signal light and the pump light, the intensity of the signal light under different delays is sampled to obtain the fundamental frequency light modulation intensity curve under different delays. Then, the pulse spectrum and phase information can be obtained through the inversion algorithm. The measurement method is simple, fast and has high measurement accuracy. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of an embodiment of a laser pulse characteristic measurement device based on fundamental frequency optical modulation sampling according to the present invention;

[0032] Figure 2 This is a graph showing the fundamental frequency optical modulation intensity curves under different delays obtained in step 1 of the measurement method embodiment of the present invention;

[0033] Figure 3 This is a schematic diagram of the spectrum and phase of the ultrashort pulse laser to be measured, obtained by the inversion algorithm in step 2 of the measurement method embodiment of the present invention.

[0034] Figure 4 This is a schematic diagram of the pulse width information obtained by the inversion algorithm in step 2 of the measurement method embodiment of the present invention.

[0035] The specific reference numerals in the attached figures are as follows:

[0036] 1-First aperture; 2-First reflecting mirror; 3-Second reflecting mirror; 4-Concave mirror; 5-Medium; 6-Obstruction; 7-Second aperture; 8-Lens; 9-Spectrometer; 10-Delay line. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0038] A laser pulse characteristic measurement device based on fundamental frequency optical modulation sampling, such as Figure 1 As shown, it includes a first aperture 1, a first reflecting mirror 2, a second reflecting mirror 3, a concave mirror 4, a medium 5, an obstruction 6, a second aperture 7, a lens 8, and a spectrometer 9.

[0039] In this embodiment, the ultrashort pulse laser under test is provided by a femtosecond laser with a center wavelength of 800 nm. A first aperture 1 is located in the incident light path of the ultrashort pulse laser under test. The first aperture 1 has a large aperture and a small aperture to split the ultrashort pulse laser under test into two beams. The transmitted light through the large aperture is used as the pump light, and the transmitted light through the small aperture is used as the signal light. The area of ​​the large aperture needs to ensure that the transmitted pump light energy is greater than 7 μJ. The area ratio of the small aperture to the large aperture can be selected between 1:25 and 1:36. In this embodiment, the area ratio of the small aperture to the large aperture is 1:36. The spacing between the small aperture and the large aperture needs to ensure that the signal light and the pump light do not interfere with each other. Based on experience, the spacing is usually greater than or equal to 2 mm, preferably 2 mm.

[0040] The second reflecting mirror 3, the concave mirror 4, the medium 5, and the obstruction 6 are sequentially located on the incident light path of the pump light. In this embodiment, a delay line 10 is provided on the second reflecting mirror 3 to change the relative delay between the signal light and the pump light. Simultaneously, the first reflecting mirror 2 and the second reflecting mirror 3 are located on the same plane when the relative delay between the signal light and the pump light is 0. In other embodiments of the invention, a delay line can also be provided on the first reflecting mirror 2 to change the relative delay between the signal light and the pump light. Preferably, the delay line 10 is formed by placing the second reflecting mirror 3 on a movable platform and moving the movable platform back and forth in a direction perpendicular to the second reflecting mirror 3. In this embodiment, the movable platform is a piezoelectric ceramic displacement stage. The invention forms the delay line 10 by moving the piezoelectric ceramic displacement stage back and forth to change the relative delay between the signal light and the pump light. In other embodiments of the invention, other forms of delay lines 10 can also be used. Meanwhile, in this embodiment, the focal length of the concave mirror 4 is 200mm, which ensures that the pump light focusing intensity is greater than 5×10⁻⁶. 12 W / cm 2 The medium 5 can be a medium material such as fused silica or SiO2. In this embodiment, fused silica with a thickness of 100μm is selected. The pump light is reflected sequentially by the second reflecting mirror 3 and the concave mirror 4, and then focused onto the surface of the medium 5 by the concave mirror 4. After being reflected by the medium 5, it is completely blocked by the object 6.

[0041] The first reflecting mirror 2, concave mirror 4, medium 5, second aperture 7, lens 8, and spectrometer 9 are sequentially located on the incident light path of the signal light. The second aperture 7 is a thin glass sheet that blocks the central region and transmits light at the edges, thus blocking the central region of the incident signal light while allowing transmission through the edges. After being reflected sequentially by the first reflecting mirror 2 and the concave mirror 4, the signal light is focused onto the surface of the medium 5 by the concave mirror 4, reflected again by the medium 5, and then transmitted through the edge region of the second aperture 7 to the lens 8, where it is focused onto the spectrometer 9. Moving the delay line 10 allows the spectrometer 9 to sample the intensity changes of the signal light at different delays.

[0042] To avoid affecting the first reflector 2 when the delay line 10 is moved, a certain gap needs to be maintained between the first reflector 2 and the second reflector 3. However, the gap between the first reflector 2 and the second reflector 3 cannot be too large, otherwise the signal light and pump light will not be able to pass through the first reflector 2 and the second reflector 3 respectively. Therefore, the present invention sets a gap of 1mm-2mm between the first reflector 2 and the second reflector 3, preferably 1mm. At the same time, in this embodiment, the first reflector 2 and the second reflector 3 are preferably D-shaped mirrors, with the two D-shaped mirrors symmetrically arranged on both sides of the gap, and the side closer to the gap is a straight edge. This design reduces the footprint of the first reflector 2 and the second reflector 3 while forming a larger light spot.

[0043] Based on the aforementioned laser pulse characteristic measurement device based on fundamental frequency optical modulation sampling, the present invention also provides a laser pulse characteristic measurement method based on fundamental frequency optical modulation sampling, specifically including the following steps:

[0044] 1) Moving the delay line 10 changes the relative delay between the signal light and the pump light. The pump light's perturbation of the signal light's optical field on the dielectric surface under different delays modulates the fundamental frequency light. The intensity of the signal light under different delays is sampled by the spectrometer 9 to obtain the following data: Figure 2 The fundamental frequency optical modulation intensity curves are shown for different delays;

[0045] 2) Based on the fundamental frequency optical modulation intensity curves under different delays, the following is obtained through the inversion algorithm: Figure 3 The diagram shows the spectrum and phase of the ultrashort pulse laser under test, and... Figure 4 The diagram shows the pulse width information.

[0046] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A laser pulse characteristic measurement device based on fundamental frequency optical modulation sampling, characterized in that: It includes a first aperture (1), a first reflecting mirror (2), a second reflecting mirror (3), a concave mirror (4), a medium (5), an obstruction (6), a second aperture (7), a lens (8), and a spectrometer (9); The first aperture (1) is located on the incident light path of the ultrashort pulse laser to be tested. The first aperture (1) has a large aperture and a small aperture to split the ultrashort pulse laser to be tested into two beams. The transmitted light through the large aperture is used as the pump light, and the transmitted light through the small aperture is used as the signal light. The area of ​​the large aperture needs to ensure that the transmitted pump light energy is greater than 7 μJ, and the area ratio of the small aperture to the large aperture is 1:25~1:36; The first reflector (2) or the second reflector (3) is provided with a delay line (10) to change the relative delay between the signal light and the pump light; the first reflector (2) and the second reflector (3) are located on the same plane when the relative delay between the signal light and the pump light is 0. The focal length of the concave mirror (4) is chosen to ensure that the pump light focusing intensity is greater than 5 × 10⁻⁶. 12 W / cm 2 ; The second reflector (3), the concave mirror (4), the medium (5) and the block (6) are located sequentially on the incident light path of the pump light; after the pump light is reflected sequentially by the second reflector (3), the concave mirror (4) and the medium (5), it is completely blocked by the block (6); The central region of the second aperture (7) is provided with a shield, and the edge region is used for transmission; The first reflector (2), the concave mirror (4), the medium (5), the second aperture (7), the lens (8) and the spectrometer (9) are located in sequence on the incident light path of the signal light; after the signal light is reflected by the first reflector (2), the concave mirror (4) and the medium (5) in sequence, it is focused onto the spectrometer (9) by the edge area of ​​the second aperture (7) and the lens (8) in sequence.

2. The laser pulse characteristic measurement device based on fundamental frequency optical modulation sampling according to claim 1, characterized in that: A gap of 1mm-2mm is maintained between the first reflector (2) and the second reflector (3); The distance between the small hole and the large hole is greater than or equal to 2 mm.

3. The laser pulse characteristic measurement device based on fundamental frequency optical modulation sampling according to claim 2, characterized in that: The first reflector (2) and the second reflector (3) are D-shaped mirrors. The two D-shaped mirrors are symmetrically arranged on both sides of the gap, and the side closer to the gap is a straight edge.

4. The laser pulse characteristic measurement device based on fundamental frequency optical modulation sampling according to claim 3, characterized in that: The gap between the first reflector (2) and the second reflector (3) is 1 mm; The distance between the small hole and the large hole is 2mm.

5. The laser pulse characteristic measurement device based on fundamental frequency optical modulation sampling according to claim 4, characterized in that: The medium (5) is fused silica or SiO2.

6. The laser pulse characteristic measurement device based on fundamental frequency optical modulation sampling according to claim 5, characterized in that: The second aperture (7) is a thin glass sheet that blocks the central area and transmits light at the edge area.

7. A laser pulse characteristic measurement device based on fundamental frequency optical modulation sampling according to any one of claims 1-6, characterized in that: The delay line (10) is formed by placing the first reflector (2) on a movable platform and moving the movable platform back and forth in a direction perpendicular to the first reflector (2); The mobile platform is a piezoelectric ceramic displacement stage.

8. A laser pulse characteristic measurement device based on fundamental frequency optical modulation sampling according to any one of claims 1-6, characterized in that: The delay line (10) is formed by placing the second reflector (3) on a movable platform and moving the movable platform back and forth in a direction perpendicular to the second reflector (3); The mobile platform is a piezoelectric ceramic displacement stage.

9. A method for measuring laser pulse characteristics based on fundamental frequency optical modulation sampling, comprising a laser pulse characteristic measuring device based on fundamental frequency optical modulation sampling as described in any one of claims 1-8, characterized in that, Includes the following steps: S1, move the delay line (10), use the pump light to perturb the light field of the signal light on the surface of the medium under different delays to form the fundamental frequency light modulation, and use the spectrometer (9) to sample the light intensity of the signal light under different delays to obtain the fundamental frequency light modulation intensity curve under different delays; S2. Based on the fundamental frequency light modulation intensity curves under different delays, the spectrum, phase, and pulse width information of the ultrashort pulse laser under test are obtained through an inversion algorithm.

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